Control apparatus for electric power steering apparatus

ABSTRACT

The present invention provides a control apparatus for an electric power steering apparatus comprises: a steering assist command value calculating section; a current control section that calculates a voltage command value; and a motor driving section that drives a motor based on the voltage command value, wherein an assist power from the motor is applied to a steering system, the control apparatus is characterized in that an SAT measuring section, that inputs an angular speed and an angular acceleration of the motor, the steering assist command value and the torque signal therein so as to estimate an SAT, is provided, and the SAT obtained by the SAT measuring section is feedbacked to the steering assist command value via a feedback section composed of a phase compensating section and a gain section.

CROSS REFERENCES TO RELATED APPLICATIONS

This is a divisional of application Ser. No. 11/813,887, filed Jul. 13,2007, which is a National Stage of International Application No.PCT/JP2006/300662 filed Jan. 12, 2006 and claims priority from JapanesePatent Application No. 2005-008100 filed Jan. 14, 2005 in the JapaneseIntellectual Property Office, Japanese Patent Application No.2005-15003, filed Jan. 24, 2005 in the Japanese Intellectual PropertyOffice, Japanese Patent Application No. 2005-23803 filed Jan. 31, 2005in the Japanese Intellectual Property Office, Japanese PatentApplication No. 2005-315602 filed Oct. 31, 2005 in the JapaneseIntellectual Property Office, the entire contents of which areincorporated herein by reference.

TECHNICAL FIELD

The present invention relates to a control apparatus for an electricpower steering apparatus in which a steering assist power from a motoris applied to a steering system of an automobile or a vehicle, andparticularly relates to the control apparatus for the electric powersteering apparatus that executes a signal process on road information,disturbance or the like in a high frequency area so as to be capable ofobtaining a safe and comfortable steering performance which provideseasy tuning.

Further, the present invention relates to a control apparatus for anelectric power steering apparatus in which a control apparatus for anelectric power steering apparatus in which a self-aligning torque (SAT)is compensated on the basis of turning and returning directions of asteering wheel.

BACKGROUND ART

An electric power steering apparatus, that applies an assist load to asteering apparatus of an automobile or a vehicle by means of rotationalforce of a motor, applies an assist load to a steering shaft or a rackshaft by transmitting a driving power of the motor using a transmissionmechanism such as gears or a belt via a speed reduction device. In orderto accurately generate an assist torque (steering assist torque), such aconventional electric power steering apparatus carries out a feedbackcontrol of motor currents. The feedback control adjusts a motor applyingvoltage so that a difference between a current command value and adetected motor current value becomes small or zero, and the adjustmentof the motor applying voltage is generally made by adjusting a dutyratio of a pulse width modulation (PWM) control.

A general constitution of the electric power steering apparatus isexplained with reference to FIG. 1. A column shaft 2 of a steering wheel1 is connected to a tie rod 6 via reduction gears 3, universal joints 4a and 4 b and a pinion rack mechanism 5. The column shaft 2 is providedwith a torque sensor 10 that detects a steering torque of the steeringwheel 1, and a motor 20 that assists a steering power of the steeringwheel 1 is connected to the column shaft 2 via the reduction gears 3. Anelectric power is supplied from a battery 14 via an ignition key 11 to acontrol unit 100 that controls the power steering apparatus, and thecontrol unit 100 operates a steering assist command value I of an assistcommand based on a steering torque signal Tr detected by the torquesensor 10 and a vehicle speed signal Ve1 detected by a vehicle speedsensor 12 so as to control an electric current to be supplied to themotor 20 based on the operated steering assist command value I.

In such an electric power steering apparatus, as disclosed in JapanesePatent Application Laid-open No. 8-290778 A, for example, conventionallya robust stabilizing compensator in the control unit 100 simultaneouslydesigns a stability of a system and sensitivity characteristics of aroad information and a disturbance information.

In the conventional control apparatus, however, since a reaction forceat a time of a steering near a steering neutral point is small, it isdifficult to accurately transmit the road information to a driver due toan influence of friction. Further, in the conventional electric powersteering apparatus, it is difficult to make a hysteresis characteristicbetween a steering angle and a steering power equivalent to acharacteristics of a hydraulic power steering.

An apparatus which solves such problems is disclosed in Japanese PatentApplication Laid-open No. 2002-369565 A.

An outline of the apparatus disclosed in Japanese Patent ApplicationLaid-open No. 2002-369565 A is explained with reference to FIG. 2related with FIG. 1. The motor 20 that generates an assist steeringpower of the steering apparatus is driven by a motor driving section 21,the motor driving section 21 is controlled by the control unit 100 shownby alternate long and two short dashes line, and the steering torquesignal Tr from the torque sensor and the vehicle speed signal Ve1 fromthe vehicle speed detecting system are inputted to the control unit 100.In the motor 20, a motor inter-terminal voltage Vm and a motor currentvalue i are measured so as to be outputted.

The control unit 100 is composed of a torque-system control section 110shown by a broken line that makes a control using the steering torquesignal Tr, and a motor-system control section 120 shown by alternatelong two short dashes line that makes a control relating to the drivingof the motor 20. The torque-system control section 110 is composed of anassist amount operating section 111, a differentiation controller 112, ayaw-rate convergence control section 113, a robust stabilizationcompensating section 114 and an SAT estimating feedback section 115. Thetorque-system control section 110 has adders 116A and 116B and asubtracter 116C. Further, the motor-system control section 120 iscomposed of a compensator 121, a disturbance estimator 122, a motorangular speed estimating section 123, a motor angular accelerationestimating section (differentiator) 124 and a motor characteristiccompensating section 125, and has adders 126A and 126B.

The steering torque signal Tr is inputted to the assist amount operatingsection 111, the differentiation controller 112, the yaw rateconvergence control section 113 and the SAT estimating feedback section115, and at this time, the vehicle speed signal Ve1 is inputted to themas a parameter. The assist amount operating section 111 operates anassist torque amount based on the steering torque signal Tr, theyaw-rate convergence control section 113 inputs the steering torquesignal Tr and an estimated value co of the motor angular speed andapplies the brake to a swing operation of the steering wheel in order toimprove the yaw convergence characteristics of the vehicle. Further, thedifferentiation controller 112 improves a responsiveness of control nearthe steering neutral point and realizes a smooth steering. The SATestimating feedback section 115 inputs the steering torque signal Tr, asignal which is obtained by adding an output from the differentiationcontroller 112 to an output from the assist amount operating section 111by means of the adder 116A, the angular speed estimated value ω which isestimated by the motor angular speed estimating section 123 and theangular acceleration estimated value *ω from the motor angularacceleration estimating section 124 therein so as to estimate the SAT,and executes a signal process on the estimated SAT using a feedbackfilter, so as to supplies the road information suitable for the steeringwheel as a reaction force.

A signal, which is obtained by adding the output from the yaw rateconvergence control section 113 to the signal obtained by adding theoutput from the differentiation controller 112 to the output from theassist amount operating section 111 by means of the adder 116B, isinputted as an assist amount AQ to the robust stabilization compensatingsection 114. The robust stabilization compensating section 114 is, forexample, a compensating section disclosed in Japanese Patent ApplicationLaid-open No. 8-290778 A, and removes a peak value at a resonancefrequency of a resonance system composed of an inertial element and aspring element included in the detected torque, and compensates a phaseshift of the resonance frequency that disturbs the responsiveness andthe stability of the control system. The subtracter 116C subtracts theoutput of the SAT estimating feedback section 115 from the output of therobust stabilization compensating section 114 so as to obtain an assistamount Ia for enabling the road information to be transmitted as thereaction force to the steering wheel.

Further, the motor angular speed estimating section 123 estimates themotor angular speed a based on the motor inter-terminal voltage Vm andthe motor current value i, and the motor angular speed ω is inputted tothe motor angular acceleration estimating section 124, the yaw rateconvergence control section 113 and the SAT estimating feedback section115. The motor angular acceleration estimating section 124 estimates amotor angular acceleration based on the inputted motor angular speed ω,and the estimated motor angular acceleration *ω is inputted to the motorcharacteristic compensating section 125. The adder 126A adds an assistamount Ia, which is obtained by subtracting the output of the SATestimating feedback section 115 from the output of the robuststabilization compensating section 114, to the output Ic of the motorcharacteristic compensating section 125, and the added signal isinputted as a current command value Ir to the compensator 121 as thedifferentiation compensator or the like. A signal, which is obtained byadding the output of the disturbance estimator 122 to the currentcommand value Ira compensated by the compensator 121 by means of theadder 126B, is inputted to the motor driving section 21 and thedisturbance estimator 122. The disturbance estimator 122 is a devicedisclosed in Japanese Patent Application Laid-open No. 8-310417 A, andcan maintain a desired motor control characteristics in an output basisof the control system based on a signal as a control target of the motoroutput which is obtained by adding the output of the disturbanceestimator 122 to the current command value Ira compensated by thecompensator 121 and the motor current value i, so that the stability ofthe control system is prevented from being lost.

A state of the torque generated between the road surface and thesteering is explained with reference to FIG. 3. When a driver steers thesteering wheel 1 so that a steering torque Th is generated, and themotor 20 generates an assist torque Tm according to the steering torqueTh. As a result, wheels are steered, and an SAT is generated as thereaction force. At this time, an inertial J and a friction (staticfriction) Fr of the motor 20 generate a torque as resistance of thesteering of the steering wheel 1. When the balance of these forces isconsidered, the following motion equation (1) is obtained:J·*ω+Fr·sign(ω)+SAT=Tm+Th  (1)When the above equation (1) whose inertial value is zero isLaplace-transformed and is solved for the SAT, the following equation(2) is obtained:SAT(s)=Tm(s)+Th(s)−J·*ω(s)−Fr·sign(ω(s))  (2)As is clear from the equation (2), when the inertial J and the staticfriction Fr of the motor 20 are previously obtained as constant, the SATcan be estimated based on the motor rotational angular speed ω, therotational angular acceleration *ω, the steering assist force and asteering signal. For this reason, the steering torque signal Tr, theangular speed ω, the angular acceleration *ω, and the output of theassist amount operating section 111 are inputted to the SAT estimatingfeedback section 115.

When the SAT information estimated by the SAT estimating feedbacksection 115 is directly feedbacked, the steering becomes too heavy, andthus steering feeling cannot be improved. For this reason, as shown inFIG. 4, the estimated value of the SAT is subject to the signal processby using a feedback filter 115A having a vehicle speed sensitive gainand a frequency characteristic, and only information which issufficiently necessary for improving the steering feeling is feedbacked.The feedback filter to be used here has a Q filter (phase delay) 115Bhaving a gain for reducing the estimated SAT to the sufficientlynecessary value as a static characteristic gain and a gain section 115Cwhich is sensitive to the vehicle speed Ve1 as shown in FIG. 5, and whenthe importance of the road information such as a stationary steering anda low-speed traveling is comparatively low, the road information to befeedbacked is reduced.

In the above apparatus disclosed in Japanese Patent Laid-open No.2002-369565 A, since the SAT functions as disturbance for the electricpower steering, the SAT is estimated by a disturbance observerconstitution. The phase delay filter (Q filter) is used for the feedbackbecause the estimated SAT as the disturbance is prevented from beingdiffused in the disturbance observer. The estimated SAT value, however,naturally becomes a value after passing the Q filter (phase delay), andthus a delay is generated in the steering transmission system.

In the apparatus disclosed in Japanese Patent Laid-open No. 2002-369565A, the SAT estimating feedback is also constituted so that a frequencyband where disturbance which is desired to be suppressed is present iscompatible with a frequency band where disturbance which is desired tobe transmitted is present, but does not have a function for positivelycanceling the disturbance which is desired to be suppressed.

On the other hand, in vehicles, brake judder and shimmy which makeuncomfortable to vehicle occupants occur at a time of a normal brakingand a stationary traveling. The brake judder means a floor/pedalvibration which is generated at the time of braking of vehicles, andoccasionally causes the vibration to a steering rotational direction.The source of the vibration is a braking torque variation generated dueto DTV (Disk Thickness Variation) of a brake disc, and the brakingtorque variation has a primary component and a high-order component of arotation of wheels. This is amplified by resonance before or aftersuspension or the like, the amplified brake judder is transmitted to avehicle body or a steering system so as to become the floor/pedalvibration or the steering vibration. Further, the shimmy is vibrationwhich is generated in the steering rotational direction when a vehicletravels, and its source is unbalance and non-unifoiniity of rotatingportions of tire wheels. The shimmy is amplified by suspension resonanceand becomes the vibration in the steering rotational direction via thesteering system.

Such the brake judder and the shimmy are not taken into consideration atall in the apparatus of Japanese Patent Laid-open No. 2002-369565 A.Japanese Patent Application Laid-open No. 2002-145075 A and JapanesePatent Application Laid-open No. 2002-161969 A disclose apparatus thatattenuate vibration due to the brake judder and the shimmy, but theymechanically cope with the brake judder and the shimmy, thereby arisingproblems such that the cost increases and fine suppression, such asvehicle speed sensitivity, cannot be performed.

Further, when the inertial and the friction of the steering system arelarge, the vibration due to the brake judder is not transmitted to thesteering wheel, but it is desirable that the inertial and the frictionof the steering system are as small as possible in order to obtain asatisfactory steering feeling and a stability of the vehicle.

Still further, the control unit 100 could be also described as FIG. 6.The steering torque value T detected by means of the torque sensor 10 tobe inputted and the vehicle speed V from the vehicle speed sensor 12 areinputted to a current command value operating section 31 for operating acurrent command value Iref. The current command value operating section31 determines the current command value Iref, which is a control targetvalue of a current supplied to the motor 20, on the basis of theinputted steering torque value T and the inputted vehicle speed V. Thecurrent command value Iref is inputted to a subtracter 32 so that adeviation I (Iref-Im) from a motor current value Im, which isfeedbacked, would be operated. The deviation is inputted to aPI-controlling section 33 for improving a specific property in asteering operation. A steering assist command value Vref improved inspecific property in the PI-controlling section 33 is inputted to aPWM-controlling section 34 to PWM-drive the motor 20 through an inverter35 provided as a driving part. The current value Im of the motor 20 isdetected by means of a motor current detector 36 to be feedbacked to thesubtracter 32. The inverter 35 includes FETs used as driving devices andcomprises a bridge circuit of the FETs.

Such an electric power steering apparatus has a self-aligning torque(SAT) function. That is to say, wheels of a vehicle automaticallyreturns to a neutral position when a driver reduces force for rotating asteering wheel or makes the force zero (namely, a hand-losing state oflosing his or her hold of the steering wheel) in a process of returningto a straight run after a changing steering. Such the SAT for returningto the neutral position becomes larger, the faster the vehicle speed is.In the electric power steering apparatus, the wheels move in a directionto the neutral position (leftward) in accordance with the SAT functionwhen the wheels are first changed rightward in the steering, forexample. The steering torque should be zero since the force for rotatingthe steering wheel by a driver is zero. Accordingly, the steering torquevalue detected by the torque sensor also becomes zero, a current is notapplied to the motor, the steering assist power is not generated, andtherefore, the wheels rotate leftward as they are connected to thesteering apparatus. The steering wheel, of course, also rotatesleftward.

The conventional electric power steering apparatus, however, has aproblem that a frictional power or the like, which corresponds to thefriction of the rotor of the motor and the frictions of the vehicle andthe steering system, deteriorates the returning of the steering wheelafter the changing steering in a low-speed run and deteriorates anon-center feeling such as a steering wheel returning feeling and afriction feeling in a high-speed run. That is to say, in a process thata driver rotates the steering wheel and changes the steering at a lowspeed to return to the straight run, the electric power steeringapparatus is so worse in returning of the steering wheel than a manualsteering apparatus or a hydraulic power steering apparatus that thedriver must rotate the steering wheel again to a direction of a straightrun in an extreme instance. Further, in a process to return to thestraight run after the changing steering for the purpose of changinglanes or correcting a direction in the high-speed run (especially in aprocess of returning in a hand-losing state without holding the steeringwheel), the wheels cannot completely return to the center position (theneutral position) even when the SAT function lets the wheels return tothe neutral position. In an extreme case, the driver must rotate thesteering wheel in a direction of the straight run once more.

As a solution method of such a problem, proposed has been a powersteering apparatus in which a road surface reaction force torquedetector is used as a steering wheel returning correcting section forcorrecting or removing the friction, a steering wheel angle detector fordetecting an angle of rotation of the steering wheel is provided as theroad surface reaction force torque detector, a steering wheel returningcorrection quantity is obtained on the basis of a steering wheel anglesignal outputted from the steering wheel angle detector and thecorrection quantity is used for adjusting imbalance in the friction,which is generated in accordance with a rotation or a direction ofmovement of the steering wheel and the steering system, in order to evena left-and-right difference of a returning property of the steeringwheel.

Similarly, also provided has been a power steering apparatus in which aroad surface reaction force torque detector as the steering wheelreturning correcting section for correcting or removing the friction isformed from a road surface reaction force torque estimating means, theroad surface reaction force torque estimating means is used forgenerating a road surface reaction force torque estimation signal byperforming a low pass filter (LPF) or a delay filter process for a valueobtained by adding the motor torque operated in terms of a steeringshaft on the basis of an output of a current detector for detecting acurrent of the motor to an output of the steering torque detector and bysubtracting the motor inertia torque in terms of the steering shaft, thesteering wheel returning correction quantity is obtained on the basis ofthe road surface reaction force torque estimation signal and thecorrection quantity is used for adjusting imbalance in the friction,which is generated in accordance with a rotation or a direction ofmovement of the steering wheel and the steering system, in order to evena left-and-right difference of a returning property of the steeringwheel.

In such conventional examples, there is a shortcoming that the steeringpower is too heavy in turning the steering wheel when the friction ofthe vehicle is large although an effect of improving returning of thesteering wheel in losing driver's hold of the steering wheel can beexpected in the case of a low speed. Generally, the manual steeringpower without the power assist in turning the steering wheel during aturn at a bend becomes a value obtained by adding the reaction forcefrom the road surface to the friction of the steering system, and thus,is heavier than the road surface reaction force by the friction. To thecontrary, the manual steering power in returning the steering wheelbecomes a value obtained by subtracting the friction of the steeringsystem from the road surface reaction force, the value being lighterthan the road surface reaction force by the friction. This mainly causesdeterioration in returning of the steering wheel. Accordingly,especially in the case of an automobile having a large value of frictionof the vehicle and the steering system, the steering wheel returningcorrection quantity for overcoming the friction to return the steeringwheel tends to increase. This causes a drawback that performing thecorrection in turning and returning with a same coefficient on the basisof the road surface reaction force results in excessively heavy power inreturning and turning the steering wheel during a turn at a bend in alow-speed run, which especially requires good returning of the steeringwheel from a position at a large steering angle, and thereby, results ingreat imbalance.

In order to solve the problems, proposed is the control apparatus forthe electric steering system disclosed in Japanese Patent ApplicationLaid-open No. 2002-29441 A. The control apparatus is the electric powersteering apparatus provided with a motor interposed in a steering torquetransmission mechanism from a steering wheel to wheels to generate atorque for assisting the steering torque by a driver, the electric powersteering apparatus comprising a steering wheel return correcting sectionfor correcting the friction of a rotor of the motor and the friction ofa vehicle and a steering system and a steering state discriminativecompensating section for discriminating the turning and returning of thesteering wheel, wherein the correction quantity of the steering wheelreturn correcting section is set to different values according to theturning and returning directions of the steering wheel.

The control apparatus disclosed in Japanese Patent Application Laid-openNo. 2002-29441 A, however, only puts a bad returning of the steeringwheel during the low speed rotation of the steering wheel in question,but does not take the SAT into account. Accordingly, the road surfacereaction force of a vehicle is so strong that the steering wheelsuddenly returns excessively in some cases. This causes a strongrequirement for the solution.

Recently, a vehicle on which an electric power steering is mounted hasbeen further increased in size. This causes a problem that a goodsteering feeling (especially turning and returning of a steering wheel)cannot be achieved in controlling a conventional small-sized vehicle.

The present invention is devised in order to solve the above problems,and an object is to provide a control apparatus for an electric powersteering apparatus that executes a signal process on road information,disturbance or the like in a frequency area without delay so as to becapable of obtaining a safe and comfortable steering performance whichprovides an easy tuning, and a brake judder and shimmy suppression.

Another object of the present invention is to provide a controlapparatus for an electric power steering apparatus with a highperformance and applicable in both of the cases that the returning ofthe steering wheel is bad and that the steering wheel excessivelyreturns by taking a self-aligning torque (SAT) into account.

DISCLOSURE OF THE INVENTION

The present invention relates to a control apparatus for an electricpower steering apparatus composed of: a steering assist command valuecalculating section that calculates a steering assist command valuebased on a torque signal from a torque sensor; an electric currentcontrol section that calculates a voltage command value based on thesteering assist command value; and a motor driving section that drives amotor based on the voltage command value, wherein an assist power fromthe motor is applied to a steering system, and the above object of thepresent invention is attained by providing the control apparatus ischaracterized in that an SAT measuring section, that inputs an angularspeed and an angular acceleration of the motor, the steering assistcommand value and the torque signal therein so as to estimate aself-aligning torque (SAT) or to measure an SAT using a sensor, and thatthe SAT obtained by the SAT measuring section is feedbacked to thesteering assist command value via a feedback section composed of a phasecompensating section and a gain section.

The present invention relates to a control apparatus for an electricpower steering apparatus that is composed of: a steering assist commandcalculating section that calculates a steering assist command valuebased on a torque signal from a torque sensor; an electric currentcontrol section that calculates a voltage command value based on thesteering assist command value; and a motor driving section that drives amotor based on the voltage command value, and an assist power of themotor is applied to a steering system, and the object of the presentinvention is achieved by providing: an SAT feedback section that inputsa motor rotational angular speed, a motor rotational angularacceleration, a steering assist power and a steering signal therein soas to estimate a self-aligning torque (SAT) or to measure an SAT using asensor, and in that the SAT value obtained by the SAT feedback sectionis added to the steering assist command value via a high pass filter anda gain section.

Further, the present invention relates to a control apparatus for anelectric power steering apparatus including a current commanding valueoperating section for operating a current command value on the basis ofa steering torque value from a steering torque detecting means and avehicle speed and a motor drive controlling section for controlling amotor for supplying a steering mechanism with a steering assist power onthe basis of a current value of the motor and the current command value,the control apparatus comprising: and the object of the presentinvention is achieved by providing: a detecting means for detecting arack shaft reaction force, a turning/returning discriminating sectionfor discriminating a turning or a returning of a steering wheel, andwherein the current commanding value is corrected on the basis of therack shaft reaction force and a result of the determination in theturning/returning discriminating section.

Still further, the present invention relates to a control apparatus foran electric power steering apparatus including a current command valueoperating section for operating a current command value on the basis ofa steering torque value from a steering torque detecting means and avehicle speed and a motor drive controlling section for controlling amotor for supplying a steering mechanism with steering assist power onthe basis of a current value of the motor and the current command value,and the object of the present invention can be achieved by providing aself-aligning torque (SAT) section for detecting or estimating an SAT, aturning/returning discriminating section for discriminating a turning ora returning of a steering wheel, and a gain section for gain-changingthe SAT in accordance with an output of the turning/returningdiscriminating section, to subtract the SAT compensating value outputtedfrom the gain section from the current command value.

Moreover, the present invention relates to a control apparatus for anelectric power steering apparatus including a current commanding valueoperating section for operating a current command value on the basis ofa steering torque value from a steering torque detecting means and avehicle speed and a motor drive controlling section for controlling amotor for supplying a steering mechanism with a steering assist power onthe basis of a current value of the motor and the current command value,and an object of the present invention can be achieved by providing anSAT section for detecting or estimating an SAT, a turning/returningdiscriminating section for discriminating a turning or a returning of asteering wheel, a gain section for gain-changing the SAT in accordancewith an output from the turning/returning discriminating section; afunction converting section for function-converting an angle speed and amultiplying section for multiplying the SAT compensating value outputtedfrom the gain section by an angle speed function outputted from thefunction converting section, to subtract a result of the multiplicationin the multiplying section from the current command value.

BRIEF DESCRIPTION OF THE DRAWINGS

In the accompanying drawings:

FIG. 1 is a diagram illustrating an example of a general steeringmechanism;

FIG. 2 is a block diagram to show a constitutional example of aconventional control unit;

FIG. 3 is a schematic diagram to show a state of a torque generatedbetween a road surface and a steering wheel;

FIG. 4 is a diagram illustrating a conventional constitutional exampleof the feedback section;

FIG. 5 is a diagram to show a characteristic example of a feedbackfilter;

FIG. 6 is a block diagram to show an example of a structure of a controlunit;

FIG. 7 is a block diagram to show a first embodiment of the presentinvention;

FIG. 8 is a block diagram to show a constitutional example of a feedbacksection to be used in the present invention;

FIG. 9 is a block diagram to show another constitutional example of thefeedback section to be used in the present invention;

FIG. 10 is a block diagram to show a second embodiment of the presentinvention;

FIG. 11 is a block diagram to show a constitutional example of afeedback section to be used in the present invention;

FIG. 12 is a block diagram to show another constitutional example of thefeedback section to be used in the present invention;

FIG. 13 is a block diagram to show a structure of a third embodiment ofthe present invention;

FIG. 14 illustrates an example of discrimination of turning andreturning in the present invention;

FIG. 15 illustrates an example of gain in a gain section;

FIG. 16 is a block diagram to show a structure of a fourth embodiment ofthe present invention;

FIG. 17 illustrates an example of a specific property of a functionconverting section;

FIG. 18 is a block diagram to show a structure of a fifth embodiment ofthe present invention;

FIG. 19 is a diagram showing a concrete example of a steering conditionsensitive gain set by a steering condition sensitive gain section;

FIG. 20 is a flowchart for explaining an operation example of thesteering condition judging section according to the present invention;

FIGS. 21A to 21C are charts showing respective concrete example of gainsset by an ω-sensitive gain section, a steering torque sensitive gainsection, a steering angle sensitive gain section; and

FIG. 22 is a flowchart for explaining an operation example of thecontrol apparatus of the electric power steering apparatus according tothe present invention.

BEST MODE FOR CARRYING OUT THE INVENTION

Various embodiments of the present invention are explained below withreference to drawings.

Since a self-aligning torque (SAT) seems to be disturbance of anelectric power steering, the SAT is estimated or measured by adisturbance observer constitution. The disturbance observer has aQ-filter (phase delay) so that estimated or measured disturbance isprevented from being diffused at the time of a feedback (for example,Japanese Patent Application Laid-open No. 2002-369565 A), but since itis not an object of the SAT feedback to cancel the SAT as disturbance,the completely same constitution as that of the disturbance observer isnot necessary. The SAT feedback is a design of disturbance sensitivity.

In the present invention, a phase-lead compensation is made on anestimated SAT value, so that a delay of a steering transmission systemis compensated. When the SAT is feedbacked without delay, linearity isgenerated in the steering force, steering feeling (direct feeling orsense of unity) as well as sense of rigidity is improved. Particularly,traveling characteristics on a low-friction road are improved. Wheninfluences of unnecessary disturbance and noise cannot be ignored at thetime of compensating a delay with a phase-lead element, a low passfilter (LPF) is disposed so as to eliminate the influences of thedisturbance and the noise. Further, since characteristics of the SAT andcharacteristics of road information which are not desired to betransmitted to drivers change due to a vehicle speed (high,intermediate, low), the feedback characteristics are changed accordingto the vehicle speed.

An embodiment (first embodiment) of the present invention is explainedwith reference to FIG. 7 related with FIG. 2. The similar or samemembers to those in FIG. 2 are designated by the same numbers, and theexplanation thereof is omitted.

In the present invention, an SAT estimating section 117 inputs asteering torque signal Tr, an angular speed ω, an angular acceleration*ω and an added result of an adder 116A (assist amount operated result)therein so as to estimate an SAT, and feedbacks the estimated SAT value*SAT via a feedback section 118 to an adder 116C. A constitution of thefeedback section 118 is as shown in FIG. 8, for example. That is to say,the feedback section 118 is composed of a phase-lead compensatingsection 118-1 as a phase compensating section that inputs the estimatedSAT value *SAT therein so as to carry out a phase-delay compensation, alow pass filter 118-2 that eliminates the disturbance and noise, and again section 118-3 that multiplies a gain K.

In such a constitution, the SAT estimating section 117 inputs thesteering torque signal Tr, the angular speed ω, the angular acceleration*ω and the added result of the adder 116A therein so as to estimate theSAT, but the estimation is performed according to the above equation(2). The estimated SAT value *SAT is inputted to the phase-leadcompensating section 118-1 in the feedback section 118, and thus a delayof the steering transmission system is compensated.

The phase-lead compensating section 118-1 is expressed as(T₂·s+1)/(T₁·s+1) where “s” is a Laplace operator by a transferfunction. The estimated SAT value *SAT, whose phase delay is compensatedby the phase-lead compensating section 118-1, is inputted to the lowpass filter 118-2 that eliminates the disturbance and the noise, and theestimated SAT value *SAT where high and intermediate frequencycomponents are eliminated is multiplied by a gain K in the gain section118-3, so as to output as an estimated SAT value *SATc. The estimatedSAT value *SATc is added to an output of the robust stabilizationcompensating section 114 by the adder 116C, so that the added value isinputted to a motor system control section 120.

As explained above, in the present invention, the delay of the steeringtransmission system is compensated by performing the phase-leadcompassion on the estimated SAT value *SAT, and when the SAT isfeedbacked without delay, the linearity is generated in the steeringforce, so that the steering feeling (direct feeling and the sense ofunity) is improved and the traveling characteristics on the low-frictionroad are improved. Further, the low pass filter 118-2 is not alwaysnecessary, but when the influences of unnecessary disturbance and noisecannot be ignored at the time when the phase-lead compensating section118-1 compensates a delay, the unnecessary disturbance and noise can beeliminated by disposing the low pass filter 118-2. Actually, since theroad information such as shimmy and flutter which are not desired to bereceived by a driver has high frequency, the disposing of the low passfilter 118-2 is effective.

On the other hand, since the SAT characteristic and the characteristicof the road information which are not desired to be received by a driverchange at the time of a low-speed traveling, an intermediate-speedtraveling or a high-speed traveling of the vehicle, the characteristicsmay be changed according to the vehicle speed signal Ve1. That is, avehicle speed sensitive type feedback section may be constituted.

FIG. 9 shows a constitutional example of the feedback section 118A inthe above case, and the vehicle speed sensitive type feedback section issuch that the phase-lead compensating section 118-1A, the low-passfilter 118-2A and the gain section 118-3A being inputted the vehiclespeed signal Ve1 therein, and the respective sections automaticallychange the characteristics according to the vehicle speed. Since the SATincreases in an intermediate speed range, for example, the phase lead ofthe phase-lead compensating section 118-1A is increased in theintermediate speed range, and since the unnecessary disturbance andnoise increase in a high speed range, a cut-off frequency of the lowpass filter 118-2A is reduced. Further, since the SAT feedback is notmuch necessary in a low speed range, the gain K of the gain section118-3A is reduced.

The vehicle speed sensitive type feedback section 118A may beconstituted so that two types of the phase-lead compensating sections118-1A are prepared for the intermediate speed and another speed, twotypes of the low pass filters 118-2A are prepared for the low speed andanother speed, and two types of the gain sections 118-3A are preparedfor the high speed and another speed so as to detect high, intermediateand low areas of the vehicle speed signal Ve1, and the respectivesections may be switched.

Although the SAT estimating section 117 estimates the SAT in the aboveembodiment, the SAT may be measured by a sensor. Only the gain section(118-3, 118-3A) may be of torque sensitive type. As a result,comfortable steering feeling can be obtained.

According to the present invention, the SAT estimating section thatestimates an SAT or the SAT measuring section that measures it using asensor is provided, and the estimated SAT value estimated by the SATestimating section or the SAT value measured by the SAT measuringsection is feedbacked to the steering assist command value via thefeedback section composed of the phase-lead compensating section and thegain section, so that the signal process can be executed on the roadinformation, disturbance or the like in the frequency area without adelay. For this reason, a control equivalent to the case where the SATis estimated can be made, and a safe and comfortable steeringperformances which prove an easy tuning can be obtained. Further, whenthe low pass filter is disposed in the feedback section, influences ofthe unnecessary disturbance and noise can be eliminated.

Further, since the phase-lead compensating section, the low pass filterand the gain section in the feedback section are sensitive to a vehiclespeed signal so as to be changed, a more safe and comfortable steeringperformance can be obtained. For example, since the SAT becomes large inthe intermediate speed range, the phase lead of the phase-leadcompensating section is increased in the intermediate speed range, sincethe unnecessary disturbance and noise increase in a high speed range,the cut-off frequency of the low pass filter is decreased, and since theSAT feedback is not much necessary in a low speed range, the gain of thegain section is reduced. For this reason, more comfortable steeringfeeling can be obtained.

In the present invention, a high pass filter is inserted into theestimated SAT value, so that a rack reaction force to be inputted fromthe outside is estimated (estimated SAT value), the motor is controlledso that a reaction force which is not desired to be transmitted to thedriver is canceled, and the brake judder and shimmy are suppressed insuch a manner. Since the estimated SAT value is positively canceled asdisturbance, the steering feeling is improved. Further, a phase-leadelement may be inserted in order to compensate the delay, and since thecharacteristic of the SAT and the characteristic of the road informationwhich are not desired to be transmitted to the driver change due to avehicle speed (high, intermediate, low), the feedback characteristic maybe changed according to the vehicle speed.

An embodiment (second embodiment) of the present invention is explainedwith reference to FIG. 10 related with FIG. 7. The similar or samemembers to those in FIG. 7 are designated by the same numbers, and theexplanation thereof is omitted.

In the present invention, an SAT estimating section 117 inputs asteering torque signal Tr, an angular speed ω, an angular acceleration*ω and an added result in an adder 116A (assist amount operated result)therein so as to estimate the SAT, and adds the estimated SAT value *SATvia a feedback section 119 to the adder 116C. A constitution of thefeedback section 119 is as shown in FIG. 11, for example. That is, thefeedback section 119 is composed of a vehicle speed sensitive-type highpass filter 119-1 that inputs the estimated SAT value *SAT therein andoutputs a high-frequency component, and a vehicle speed sensitive-typegain section 119-3 that multiplies a gain G. The high-pass filter 119-1can be composed of a transfer function including a high-pass filtercharacteristic.

In such a constitution, the SAT estimating section 117 inputs thesteering torque signal Tr, the angular speed ω, the angular acceleration*ω and the added result in the adder 116A therein so as to estimate theSAT, but the estimation is performed according to the above equation(2). The estimated SAT value *SAT is inputted to the high pass filter119-1 in the feedback section 118, and thus only a high-frequencycomponent relating to brake judder and shimmy passes therethrough, sothat the brake judder and shimmy can be suppressed. An output of thehigh pass filter 119-1 through which only the high-frequency componentpasses is inputted to the gain section 119-3, and the output ismultiplied by a gain G, so as to output as the estimated SAT value*SATc. The estimated SAT value *SATc is added to an output (currentcommand value) of a robust stabilization compensating section 114 by anadder 116D, and the added value is inputted to the motor system controlsection 120.

Conventionally (Japanese Patent Application Laid-open No. 2002-369565A), although the Q filter (phase delay) is inserted so that thedisturbance is prevented from being diffused at the time of thefeedback, and thus the motor does not amplify uncomfortable vibrationfrom a road surface, this does not mean that the uncomfortable vibration(brake judder and shimmy) is canceled. For this reason, in the presentinvention, the estimated SAT value *SAT as an estimated reaction forcevalue is allowed to pass through the high pass filter 119-1, and areaction force component which is not desired to be transmitted to thedriver is extracted and is added to the current command value so that acorrection is made. As a result, the reaction force component which isnot desired to be transmitted to the driver can be canceled. When theestimated SAT value *SAT is directly added, satisfactory suppressioncannot be carried out, and thus the estimated SAT value *SAT ismultiplied by the gain G so as to be added. Further, the estimated SATvalue *SAT may be subjected to the phase compensation. Further, when theinfluences of the unnecessary disturbance and noise cannot be ignored,the low pass filter is disposed so as to be capable of eliminating theunnecessary disturbance and noise.

Further, since the SAT characteristic, the uncomfortable vibration andthe characteristic of the road information which are not desired to bereceived by the driver change according to a rotation number (speed) oftires at the time of a low-speed traveling, an intermediate-speedtraveling or a high-speed traveling of the vehicle, the filtercharacteristic and the gain G may be switched according to the vehiclespeed signal Ve1. That is, a vehicle speed sensitive-type feedbacksection may be constituted. In this case, a cut-off frequency of thehigh pass filter 119-1 is heightened and the gain G is increased at thetime of the high speed, and the cut-off frequency of the high passfilter 119-1 is reduced and the gain G is reduced at the time of the lowspeed. In such an active vibration control, the control system should bedesigned suitably or vibration is heightened. For this reason, a signalfrom an external controller (for example, an ABS controller) isutilized, and a correction may be made only when a vibration is easilygenerated due to braking at the time of the high-speed traveling or thelike.

As explained above, in the present invention, the high pass filter 119-1is inserted into the estimated SAT value *SAT, and the gain is adjustedby the gain section 119-3 so that the SAT is feedbacked. For thisreason, the brake judder and shimmy can be suppressed.

FIG. 12 shows another constitutional example of the feedback section 119according to the present invention. A system which is comprised theQ-filter 119-2 and the gain section (gain G1) 119-4 which are similar toconventional ones is connected to a system which is comprised the highpass filter 119-1 composed of input/output of the Q-filter 119-2 and thegain section (gain G2) 119-5 in parallel, and outputs of the respectivesystems are added by the adder 119-6 so that the added value is added tothe current command value. According to the above example, an effect bythe conventional correction of a low frequency and an effect based onthe high pass filter 119-1 can be produced, namely, the road informationwhich is not desired to be transmitted to the driver is suppressed, andthe road information which is desired to be transmitted to the driver ismaintained so that the comfortable steering feeling can be obtained.

Even in this example, the Q-filter 119-2, and the gain sections 119-4and 119-5 can be of the vehicle speed sensitive type.

Although the SAT is estimated by the SAT estimating section 117 in theabove embodiment, the SAT may be obtained by measuring it by a sensor.

Further, only the gain sections (119-3, 119-4 and 119-5) may be oftorque sensitive type. As a result, the comfortable steering feeling canbe obtained.

According to the present invention, the SAT estimating section thatestimates the SAT or the SAT measuring section that measures it using asensor is provided, and the estimated SAT value estimated by the SATestimating section or the SAT value measured by the SAT measuringsection is added to the steering assist command value via the feedbacksection comprised the high pass filter and the gain section, so that asignal process can be executed on the road information, the disturbanceor the like in the high frequency area. For this reason, the brakejudder and shimmy can be suppressed, and a safe and comfortable steeringperformances which prove easy tuning can be obtained.

Further, not only the brake judder and shimmy but also behavior of thesteering wheel such as kickback can be reduced, so that the comfortablesteering feeling can be provided.

FIG. 13 shows an embodiment (third embodiment) of the present inventionso as to correspond to FIG. 6. A steering torque value T from a torquesensor is inputted to a current command value operating section 31 and aturning/returning discriminating section 40. The vehicle speed V fromthe vehicle speed sensor is inputted to the current command valueoperating section 31. A current command value Iref operated in thecurrent command value operating section 31 is inputted to a subtracter43. To the turning/returning discriminating section 40, inputted is ameasured or estimated angle speed ω. A discrimination signal DSdiscriminated in the turning/returning discriminating section 40 isinputted to a gain section 42. An SAT measured or estimated in an SATsection 41 is increased G-times (G·SAT) in the gain section 42 to beinputted to the subtracter 43. A result of the subtraction in thesubtracter 43 (Iref-G·SAT) is inputted to an adder 44 as the currentcommand value Iref. To the adder 44, also inputted is a compensationsignal CM from a compensating section 50 for improving a specificproperty.

The compensating section 50 adds an inertia 51 and a convergence 52 inthe adder 53 to input a result of the addition to the adder 44 as thecompensation signal CM. The result (Iref1+CM) of the addition in theadder 44 is inputted to the subtracter 32 as a current command valueIref2 to be used for controlling the motor 20 through a PI controllingsection 33, a PWM controlling section 34 and an inverter 35.

The turning/returning discriminating section 40 discriminates that thesteering wheel is in a turning state when signs of the steering torquevalue T and the angle speed ω are same while it discriminates that thesteering wheel is in a returning state when the signs of the steeringtorque value T and the angle speed ω are different, as shown in FIG. 14,to output the determination signal DS of the two values (for turning andreturning states). Further, as described in Japanese Patent ApplicationLaid-open No. 2003-170856 A, it may be discriminated that the steeringwheel is in a turning state in the case that the signs of the steeringtorque value T and a steering torque changing ratio are same and anabsolute value of the steering torque changing ratio is a predeterminedvalue or more while it is discriminated that the steering wheel is in areturning state in the case that signs of the steering torque value Tand the steering torque changing ratio are different and the absolutevalue of the steering torque changing ratio is a predetermined value ormore. That is, the turning and returning states can be discriminatedonly on the basis of the steering torque value T without using the anglespeed ω.

Moreover, the SAT may be estimated by means of an external disturbanceobserver structure on the basis of a motor rotation signal and a motorcurrent command value, as disclosed in Japanese Patent ApplicationLaid-open No. 2002-274405 A, for example.

In such a structure, the motor 20 is controlled on the basis of thecurrent command value Iref operated in the current command valueoperating section 31. In the present invention, however, the currentcommand value Iref1 (=Iref−G·SAT) is obtained by subtracting theself-aligning torque “G·SAT”, which is obtained by increasing theself-aligning torque SAT which is being gain G-times in the gain section42, from the current command value Iref while the current command valueIref1 (=Iref1+CM) is obtained by adding the compensation signal CM tothe current command value Iref1. The gain G of the gain section 42 isswitched in accordance with the discrimination signal DS of theturning/returning discriminating section 40. A plus gain G is given inthe case of returning while a minus gain G is given in the case ofturning, in accordance with the discrimination signal DS of two values.That is, the gain in turning is set to “0” when the gain in returning is“−1.0” while the gain in turning is set to “+0.2” when the gain inreturning is “−0.8”, as shown in FIG. 15. Accordingly, when the steeringwheel is returned too much, a minus gain is multiplied only inreturning, and thus, the power steering operates to brake the returningof the steering wheel caused by the road surface reaction force. In thecase of turning, the steering power is reduced since a plus gain ismultiplied before subtraction.

FIG. 16 shows another embodiment (forth embodiment) of the presentinvention so as to correspond to FIG. 13. The problem to be solved issudden rotation of the steering wheel due to the excessively strong roadsurface reaction force. For the purpose of solving the problem, afunction converting section 45 for the angle speed ω is provided in FIG.16 so that the function-converted angle speed f(ω) would be multipliedby the compensation value “G·SAT” of the self-aligning torque SAT in themultiplying section 46 to be inputted to the subtracter 43. In thiscase, a specific property of the function converting section 45 is afirst-order lag function as shown in FIG. 17, so that the large gain inhigh-speed rotation operates as a brake while the gain is made small inlow-speed rotation for the purpose of preventing the unnecessary assisttorque from being generated. This is because the road surface reactionforce is considered to be small in a low-speed rotation although thedriver holds the steering wheel by his or her hands.

In such a structure, the self-aligning torque SAT is increased gainG-times in accordance with a discrimination result of theturning/returning discriminating section 40 and the self-aligning torque“G·SAT” is inputted to the multiplying section 46, similarly to theembodiment in FIG. 13. The angle speed ω is function-converted f(ω) inthe function converting section 45 to be inputted to the multiplyingsection 46 and the angle speed is multiplied by the self-aligning torque“G·SAT” from the gain section 42 to be inputted to the subtracter 43. Inthe subtracter 43, an output of the multiplying section 46 (=G·SAT·f(ω))is subtracted from the current command value Iref1 to generate thecurrent command value Iref1 while the compensation signal CM from thecompensating section 50 is added to the current command value Iref1 inthe adder 44 to generate the current command value Iref2 (=Iref1+CM).

As described above, in accordance with the embodiment, the SATcompensating value is multiplied by the gain f(ω) responding to thesteering speed (ω). Accordingly, the large gain in a high-speed rotationcan operate as a brake while the small gain in a low-speed rotationprevents the unnecessary assist torque from being generated. Further,the steering torque is small when the returning of the steering wheel inrunning on a low friction road or the like is small in force. Thisallows a good balance and a good steering feeling to be achieved.

The function in the function converting section may be a linear functionalthough it is a first-order lag function in the above embodiments.

According to the present invention, the SAT is increased gain-times bymeans of plus or minus gain in accordance with a result ofdiscrimination of turning or returning of the steering wheel so that thesignal thereof would be subtracted form the current command value. Thisallows the returning of the steering wheel due to the road surfacereaction force to be braked, so that the steering wheel does notexcessively return. Thus, a power steering apparatus with a highperformance can be achieved.

In accordance with the control apparatus for an electric power steeringapparatus according to the present invention, a control is performed sothat multiplying a minus gain only in returning of a steering wheelwould allow the returning of the steering wheel, which is caused by theroad surface reaction force, to be braked by means of the powersteering, so that the steering wheel does not return excessively.Further, it is arranged that a large gain operate as a brake in ahigh-speed rotation while a small gain prevent the unnecessary assisttorque from being generated in a low-speed rotation. This causes nosudden rotation of a steering wheel due to excessively strong roadsurface reaction force.

In the present invention, the SAT is taken into account to controlreturning of the steering wheel, so that a good steering feeling can beachieved not only in a small-sized automobile but also in a large-sizedautomobile.

In a fifth example of the present invention, when a steering angleresponse gain and/or a steering torque response gain are/is provided, atthe time of on-center where the self-aligning torque (SAT) is small(steering torque is small/steering angle is small) and at the time ofoff-center where the self-aligning torque is large (steering torque islarge/steering angle is large), suitable SAT compensating values can beset. In the present invention, a steering state (turning steering,returning steering, steering holding) is determined, so that the SATcompensating value can be set at the time of the steering holding state.In other words, in the fifth example of the present invention, the SATcompensating values are suitably set at the time of on-center,off-center and steering holding states by using the determined result ofthe steering state (turning steering, returning steering, steeringholding), a steering angular speed signal, a steering torque signal anda steering angle signal.

The example of the present invention in FIG. 18 is related with FIG. 13,a steering torque value T from the torque sensor (not shown) is inputtedto a current command value operating section 31 and also to a steeringstate determining section 61. A vehicle speed V from a vehicle speedsensor (not shown) is inputted to the current command value operatingsection 31 and also to a vehicle speed sensitive gain section 60. Acurrent command value Iref, which is operated by the current commandvalue operating section 31 based on the steering torque value T and thevehicle speed V, is inputted to a subtracter 43.

A self-aligning torque SAT, which is detected or estimated by an SATsection 41, is inputted to a multiplying section 70. The vehicle speedsensitive gain section 60 sets a vehicle speed sensitive gain G₁ basedon the vehicle speed V. Also a vehicle speed sensitive gain G₁ from thevehicle speed sensitive gain section 60 is inputted to the multiplyingsection 70. An output “SAT·G₁” of the multiplying section 70 is inputtedto a multiplying section 71.

On the other hand, a measured or estimated steering angular speed ω(motor speed) is inputted to the steering state determining section 61.The steering state determining section 61 determines the steering state(turning steering, returning steering or steering holding) based on thesteering torque value T and the steering angular speed ω, and outputs adetermined signal (signal representing the steering state) as adetermined result to a steering state sensitive gain section 63.

The steering state sensitive gain section 63 switches a steering statesensitive gain G2 based on the determined signal from the steering statedetermining section 61. Namely, the steering state sensitive gain G2which is outputted from the steering state sensitive gain section 63 toa multiplying section 71 is switched according to the determined signalfrom the steering state determining section 61.

FIG. 19 illustrates a specific example of the steering state sensitivegain G₂. The steering state sensitive gain section 63 determinespatterns A to C shown in FIG. 19, for example.

(1) Pattern A:

This pattern A means that “the steering state sensitive gain G₂ isoperated only at the time of a turning steering” in the following state.The steering state sensitive gain G₂ in the case where the turningsteering is determined is set to a negative value (for example, thevalue of the steering state sensitive gain G₂ is set to “−1” or “−0.5”),the steering state sensitive gain G₂ in the case where the turningsteering is determined is set to “0”, and the steering state sensitivegain G₂ in the case where the steering holding is determined is set to“0”.

(2) Pattern B:

This pattern B means that “the steering state sensitive gain G₂ isoperated only at the time of a turning steering” in the following state.The steering state sensitive gain G₂ in the case where the turningsteering is determined is set to “0”, the steering state sensitive gainG₂ in the case where the turning steering is determined is set to apositive value (for example, the value of the steering state sensitivegain G₂ is set to “1” or “2”), and the steering state sensitive gain G₂in the case where the steering holding is determined is set to “0”.

(3) Pattern C:

In this pattern C, “the steering state sensitive gain G₂ is operatedonly at the time of a steering holding” in the following state. Thesteering state sensitive gain G₂ in the case where the turning steeringis determined is set to “0”, the steering state sensitive gain G₂ in thecase where the turning steering is determined is set to “0”, and thesensitive gain G₂ in the case where the steering holding is determinedis set to a positive value (for example, the value of the steering statesensitive gain G₂ is set to “1” or “5”).

The above-mentioned some patterns can be combined, and the value of thesteering state sensitive gain G2 can be freely set.

An output “SAT·G₁·G₂” from the multiplying section 71 is inputted to amultiplying section 72. An ω-sensitive gain G₃(ω) set by an ω-sensitivegain section 64 is also inputted to the multiplying section 72. Anoutput “SAT·G₁·G₂·G₃(ω)” of the multiplying section 72 is inputted to amultiplying section 73. A steering torque sensitive gain G₄(T) set by asteering torque sensitive gain section 65 is also inputted to themultiplying section 73. An output “SAT·G₁·G₂·G₃(ω)·G₄(T)” of themultiplying section 73 is inputted to a multiplying section 74. Asteering angle sensitive gain G₅(θ) set by a steering angle sensitivegain section 66 is also inputted to a multiplying section 74. An output“SAT·G₁·G₂·G₃(ω))·G₄(T)·G₅(θ)” of the multiplying section 74, namely, anSAT compensating value in the present invention is inputted to asubtracter 43. A subtracted result (Iref−SAT compensating value) fromthe subtracter 43, namely, (Iref−SAT·G₁·G₂·G₃(ω))·G₄(T)·G₅(θ)) isinputted as a current command value Iref1 to an adder 44, and acompensating signal CM from a compensating section 50 for improving acharacteristic is also inputted to the adder 44.

The compensating section 50 adds an inertia 51 and a convergence 52using an adder 53, and inputs an added result as the compensating signalCM to the adder 44. An added result (Iref1+CM) in the adder 44 isinputted as a current command value Iref1 to a subtracter 32, and amotor 20 is controlled via a PI control section 33, a PWM controlsection 34 and an inverter 35.

A steering state determining section 61 determines whether the steeringangular speed ω obtains continuously the same value (or a value in acertain range) for a constant time period as shown in a flowchart ofFIG. 20 (Step S31). When the determination is made that the same valuecontinues, a steering holding is determined (Step S32). On the otherhand, when the determination is made that the same value does notcontinue, a steering is determined (Step S33), and a determination ismade whether a code of the steering torque value T matches a code of thesteering angular speed ω (Step S34). When the determination is made thatthe code of the steering torque value T matches the code of the steeringangular speed ω, the turning steering is determined (Step S35). On theother hand, when the code of the steering torque value T does not matchthe code of the steering angular speed ω, the returning steering isdetermined (Step S36).

In short, the steering state determining section 61 outputs ternaryvalue (turning steering, returning steering, steering holding)determined signals to the steering state gain section 63 according to anoperation shown in the flowchart of FIG. 20.

Further, in the case where the steering state determining section 61does not determine the steering holding but determines only the turningsteering and the returning steering, as described in Japanese PatentApplication Laid-Open No. 2003-170856 A, when the code of the steeringtorque value T is identical to the code of a steering torque change rateand an absolute value of the steering torque change rate is not lessthan a predetermined value, the turning steering may be determined. Whenthe code of the steering torque value T is different from the code ofthe steering torque change rate and the absolute value of the steeringtorque change rate is not less than a predetermined value, the returningsteering may be determined. That is to say, the steering statedetermining section 61 can determine the turning steering and thereturning steering using only the steering torque value T without usingthe steering angular speed ω.

In the SAT section 41, the self-aligning torque SAT may be estimated bya disturbance observer structure using a motor rotation signal and amotor current command value as described in, for example, JapanesePatent Application Laid-Open No. 2002-274405 A.

Further, the ω-sensitive gain section 64 sets the ω-sensitive gain G₃(ω)based on the steering angular speed signal ω. A specific example of theω-sensitive gain G₃(ω) includes a primary delay function G₃(ω) of thesteering angular speed signal ω shown in FIG. 21A, for example. Thesteering torque sensitive gain section 65 sets the steering torquesensitive gain G₄(T) based on the steering torque signal T. A specificexample of the steering torque sensitive gain G₄(T) includes a primarydelay function G₄(T) of the steering torque signal T shown in FIG. 21B,for example. The steering angle sensitive gain section 66 sets thesteering angle sensitive gain G₅(θ) based on a steering angular signalθ. A specific example of the steering angle sensitive gain G₅(θ)includes a primary delay function G₅(θ) of the steering angular signal θshown in FIG. 21C, for example.

A primary function may be used instead of the primary delay functionsG₃(ω), G₄(T) and G₅(θ) used in the ω-sensitive gain section 64, thesteering torque sensitive gain section 65 and the steering anglesensitive gain section 66.

An operation example of the control apparatus is shown in a flowchart ofFIG. 22. Namely, in the present invention shown in FIG. 22, theself-aligning torque SAT is estimated by the SAT section 41 (Step S1).The vehicle speed sensitive gain section 60 calculates the vehicle speedsensitive gain G1 based on the vehicle speed V (Step S2). The steeringstate determining section 61 determines the steering state (turningsteering, returning steering, steering holding), and outputs adetermined signal (Step S3).

The steering state sensitive gain section 63 calculates the steeringstate sensitive gain G2 according to the determined signal (Step S4).The ω-sensitive gain section 64 calculates the ω-sensitive gain G₃(ω)based on the steering angular speed signal ω (Step S5). The steeringtorque sensitive gain section 65 calculates the steering torquesensitive gain G₄(T) based on the steering torque signal T (Step S6).The steering angle sensitive gain section 66 calculates the steeringangle sensitive gain G₅(θ) based on the steering angle signal θ (StepS7).

The self-aligning torque SAT, the vehicle speed sensitive gain G₁, thesteering state sensitive gain G₂, the ω-sensitive gain G₃(ω), thesteering torque sensitive gain G₄(T), and the steering angle sensitivegain G₅(θ) are calculated, so that the SAT compensating value can becalculated. That is to say, a relationship: SAT compensatingvalue=SAT·G₁·G₂·G₃(ω))·G₄(T)·G₅(θ) is established (Step S8).

When the control apparatus of the electric power steering apparatusaccording to the present invention is used, the SAT compensating valueis controlled in the on-center and off-center states. For this reason,the design of steering torque hysteresis widths (SAT compensatingvalues), which are suitable at the time of on-center and off-center canbe controlled, and the steering state (turning steering, returningsteering, steering holding), is determined. As a result, the design of asteering torque hysteresis width (SAT compensating value) at the time ofsteering holding can be also controlled.

In the control apparatus of the electric power steering apparatusaccording to the present invention, for example in the ease where thesteering angular speed is low such as hands free after the steeringangle is inputted at the time of running, the steering angular speedsensitive gain, the steering torque sensitive gain and the steeringangle sensitive gain are simultaneously used, so that the SATcompensating value is adjusted. For this reason, only convergency can beimproved without deteriorating the return of a steering wheel.

When a tuning is carried out so that the self-aligning torque (steeringtorque) increases at the time of on-center (namely, the steering torqueis small or the steering angle is small), a driver feels loss ofresistance at the time of operating the steering wheel right and left atsmall steering angles little by little. In the present invention, whenthe steering angular speed is high, the steering angular speed sensitivegain is used, and thus the self-aligning torque compensating value isset so that the steering torque (the feel of resistance) increases,namely, feeling of stickiness increases. For this reason, the loss ofresistance can be prevented.

That is to say, in the control apparatus of the electric power steeringapparatus according to the present invention, the steering angular speedsensitive gain, the steering torque sensitive gain and the steeringangle sensitive gain are used, so that the loss of steering resistancecan be prevented at the time of operating the steering wheel right andleft at small steering angles little by little during a traveling. Thepresent invention has the effect equivalent to that of a hydraulic powersteering (non-return valve).

In the present invention, the self-aligning torque is compensated basedon the steering state (turning steering, returning steering or steeringholding), the steering angular speed (motor speed), the steering angleand the steering torque. For this reason, the satisfactory steeringfeeling can be realized at the time of on-center, off-center andsteering holding not only in small-sized vehicles but also inlarge-sized vehicles.

1. A control unit for an electric power steering apparatus, the controlunit comprising a steering assist command value calculating section thatcalculates a steering assist command value based on a steering torquesignal from a torque sensor; a current control section that calculates avoltage command value based on the steering assist command value; amotor driving section that drives a motor based on the voltage commandvalue, wherein an assist power from the motor is applied to a steeringsystem; a self-aligning torque (SAT) estimating section that estimatesor measures an SAT based on an angular speed and an angular accelerationof the motor, the steering assist command value and the steering torquesignal; and an SAT feedback section that feeds back an SAT signalobtained by the SAT estimating section to the steering assist commandvalue; wherein the SAT feedback section comprises: a steering statedetermining section to determine a steering state based on the steeringtorque signal and the angular speed; and a gain section to adjust a gainin response to the steering state, and the gain from the gain section ismultiplied with the SAT signal.
 2. The control unit for an electricpower steering apparatus according to claim 1, wherein a compensationvalue of a function according to the angular speed outputted from afunction converting section is multiplied with the SAT signal.
 3. Thecontrol unit for an electric power steering apparatus according to claim1, wherein a characteristic of the steering state determining sectionchanges according to a vehicle speed signal.
 4. The control unit for anelectric power steering apparatus according to claim 1, wherein a signalobtained by multiplying a gain of the gain section with the SAT signalis further multiplied with a gain of a steering angle sensitive gainsection which changes according to a steering angle signal.
 5. Thecontrol unit for an electric power steering apparatus according to claim1, wherein a signal obtained by multiplying a gain of the gain sectionwith the SAT signal is further multiplied with a gain of a steeringtorque sensitive gain section which changes according to the steeringtorque signal.
 6. The control unit for an electric power steeringapparatus according to claim 1, wherein a signal obtained by multiplyinga gain of the gain section with the SAT signal is further multipliedwith a gain of a steering angular speed sensitive gain section whichchanges according to a steering angular speed signal.